More than 7% of the US population who have diabetes are at a 2 to 6-fold higher risk for having ischemic stroke and suffer from unfavorable stroke outcome and poor recovery. Reperfusion therapy with tissue plasminogen activator (tPA) is the only therapy for ischemic stroke; however, this treatment increases the risk of bleeding into the brain (hemorrhagic transformation, HT), especially in diabetics. A critical barrier to progress in the development of new therapeutic strategies, as well as the proper use of tPA in high-risk populations, is the lack of understanding on how bleeding influences the repair and recovery after stroke. Our goal is to identify new targets for prevention and treatment of stroke in patients with preexisting vascular disease and develop new neurovascular protection strategies. Our objective is to address this critical barrier and clinical problem by defining the impact and mechanisms by which HT impairs neurovascular repair after ischemic stroke in diabetes. Our central hypothesis is that bleeding into the brain, petechial OR spaceoccupying, impairs neurovascular restoration and worsens outcome in diabetes via the activation of toll like receptor (TLR)-4 by excess iron, a novel damage associated molecular pattern (DAMP). This hypothesis will be tested in 3 Specific Aims: 1. Test the hypothesis that petechial nonspace-occupying HT impairs neurovascular restorative repair and worsens neurological deficits in diabetes. We will determine the extent to which HT impairs neurovascular repair and functional outcome in multiple models of stroke and diabetes; 2. Test the hypothesis that iron deposition resulting from greater HT in diabetes impairs neurovascular plasticity and worsens outcome of ischemic stroke. We will determine the role of iron on neurovascular restoration and functional outcome after embolic stroke in Type 2 diabetes; and 3. Test the hypothesis that HT stimulates TLR4 signaling/inflammation worsening repair and recovery after diabetic ischemic stroke. We will determine the mechanisms by which HT impairs functional recovery after embolic stroke in Type 2 diabetes. The outcomes of our translational studies include: 1) demonstrating that any bleeding into the brain is detrimental by impairing vascular and neuronal repair (this challenges the existing paradigm that only space-occupying HT worsens outcomes); 2) generating new and important data related to mechanisms of how diabetes attenuates neuronal and endothelial repair processes by using combinations of animal models of diabetes or stroke to recapitulate the clinical condition, and 3) identification of iron as a new DAMP and show that iron chelation and/or downstream TLR4 inhibition are promising therapeutic targets in stroke treatment/recovery. This project will have a significant positive impact on stroke research and human health because it will 1) identify neurovascular protection & restoration strategies to improve stroke outcomes, 2) advance our knowledge of the role of the cerebral vasculature in stroke repair, and 3) provide specific information on stroke recovery in diabetes which occurs in more than 30% of the 800,000 annual stroke victims.